diff --git a/backup.nix b/backup.nix
index b74d6b5..cb11c1c 100644
--- a/backup.nix
+++ b/backup.nix
@@ -27,7 +27,7 @@ let
 
     text = ''
       source "${backupConfigFile}"
-      pg_dump misskey | gzip | s3cmd put --config "$S3CFG" - "s3://$MISSKEY_BACKUP_BUCKET/$MISSKEY_BACKUP_PREFIX/misskey-pgdump-$(date --iso-8601).sql.gz"
+      pg_dump misskey | gzip | s3cmd put --config "$S3CFG" - "s3://$MISSKEY_BACKUP_BUCKET/\$\{MISSKEY_BACKUP_PREFIX}misskey-pgdump-$(date --iso-8601).sql.gz"
     '';
   };
 in {